Intraluminal microneurography probe

ABSTRACT

An intraluminal microneurography probe has a probe body that is configured to be introduced into an artery near an organ of a body without preventing the flow of blood through the artery. An expandable sense electrode and an expandable stimulation electrode are fixed to the probe body at one end of each electrode such that movement of the other end toward the fixed end causes the sense electrode to expand from the probe body toward a wall of the artery. A ground electrode is configured to couple to the body, and a plurality of electrical connections are operable to electrically couple the electrodes to electrical circuitry. The sense electrode is operable to measure sympathetic nerve activity in response to excitation of the stimulation electrode. An ablation element is located between the expandable sense electrode and expandable stimulation electrode, and is operable to ablate nerves proximate to the artery.

This application claims the benefit of U.S. Provisional Application No.62/192,340 filed Jul. 14, 2015, the contents of which are hereinincorporated by reference.

FIELD

The invention relates generally to neural measurement, and morespecifically to an intraluminal microneurography probe.

BACKGROUND

The human body's nervous system includes both the somatic nervous systemthat provides sense of the environment (vision, skin sensation, etc.)and regulation of the skeletal muscles, and is largely under voluntarycontrol, and the autonomic nervous system, which serves mainly toregulate the activity of the internal organs and adapt them to thebody's current needs, and which is largely not under voluntary control.The autonomic nervous system involves both afferent or sensory nervefibers that can mechanically and chemically sense the state of an organ,and efferent fibers that convey the central nervous system's response(sometimes called a reflex arc) to the sensed state information. In somecases, the somatic nervous system is also influenced, such as to causevomiting or coughing in response to a sensed condition.

Regulation of the human body's organs can therefore be somewhatcharacterized and controlled by monitoring and affecting the nervereflex arc that causes organ activity. For example, the renal nervesleading to the kindey can often cause a greater reflexive reaction thandesired, contributing significantly to hypertension. Measurement of thenerve activity near the kidney, and subsequent ablation of some (but notall) of the nerve can therefore be used to control the nervous system'soverstimulation of the kindey, improving operation of the kidney and thebody as a whole.

Because proper operation of the nervous system is therefore an importantpart of proper organ function, it is desired to be able to monitor andchange nervous system function in the human body to characterize andcorrect nervous system regulation of internal human organs.

SUMMARY

One example embodiment of the invention comprises an intraluminalmicroneurography probe, having a probe body that is substantiallycylindrical and that is configured to be introduced into an artery nearan organ of a body without preventing the flow of blood through theartery. An expandable sense electrode is fixed to the probe body at oneend of the sense electrode and is movable relative to the probe body ata second end of the sense electrode such that movement of the movableend toward the fixed end causes the sense electrode to expand from theprobe body toward a wall of the artery, and an expandable stimulationelectrode is fixed to the probe body at one end of the stimulationelectrode and movable relative to the probe body at a second end of thestimulation electrode such that movement of the movable end toward thefixed end causes the sense electrode to expand from the probe bodytoward a wall of the artery. A ground electrode configured to couple tothe body, and a plurality of electrical connections are operable toelectrically couple at least the expandable sense electrode, expandablestimulation electrode, and ground electrode to electrical circuitry.

In further examples, the sense electrode wire is equal to or smallerthan 10 thousandths of an inch in a direction of nerve propagation, andat least one of the expandable sense electrode and the expandablestimulation electrode comprises an expandable mesh or an expandable wirehelix. In another example, the diameter of the probe body is 2 mm orless, such that blood flow is not blocked by introduction of the probeinto the artery.

In another example nerve activity associated with a body organ ischaracterized by introduction of a probe into artery to a locationproximate to the body organ, and expansion of an expandable senseelectrode and an expandable stimulation electrode comprising a part ofthe probe to contact the artery wall while permitting blood flow aroundthe expanded sense and stimulation electrodes. An electricity sourcecoupled to the stimulation electrode is used to excite the stimulationelectrode, and the expanded sense electrode is used to measuresympathetic nerve activity as a result of exciting the stimulationelectrode.

In a further example, ablation of nerves in the vicinity of the locationproximate to the body organ is performed such as via an ablation elementcomprising a part of the probe, and re-excitation of the stimulationelectrode using an electricity source coupled to the stimulationelectrode, and re-measurement of sympathetic nerve activity as a resultof exciting the stimulation electrode using the expanded sense electrodeare performed to confirm the effects of the ablation

The details of one or more examples of the invention are set forth inthe accompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an intraluminal microneurography probe havingexpandable helical wire electrodes, consistent with an example.

FIG. 2 illustrates an intraluminal microneurography probe havingexpandable wire mesh electrodes, consistent with an example.

FIG. 3 shows introduction of an intraluminal microneurography probe intoan artery in a location near a kidney, consistent with an example.

FIG. 4 shows an intraluminal microneurography probe and sheath assemblycoupled to associated instrumentation, consistent with an example.

FIG. 5 shows spontaneous nerve activity, measured from the wall of therenal artery of an explanted kidney, consistent with an example.

FIG. 6 shows spontaneous nerve activity in the wall of the renal arteryof an explanted kidney using an intraluminal microneurography probe,consistent with an example.

FIG. 7, shows a stimulus signal and the resulting measured RSNA actionpotential, consistent with an example.

FIG. 8 shows destruction of the renal sympathetic nerves and theresulting effects on RSNA signals measured as a result of an appliedstimulus signal, consistent with an example.

FIG. 9 is a flowchart illustrating a method of using an intraluminalmicroneurography probe to treat a medical condition, consistent with anexample.

DETAILED DESCRIPTION

In the following detailed description of example embodiments, referenceis made to specific example embodiments by way of drawings andillustrations. These examples are described in sufficient detail toenable those skilled in the art to practice what is described, and serveto illustrate how elements of these examples may be applied to variouspurposes or embodiments. Other embodiments exist, and logical,mechanical, electrical, and other changes may be made. Features orlimitations of various embodiments described herein, however importantto the example embodiments in which they are incorporated, do not limitother embodiments, and any reference to the elements, operation, andapplication of the examples serve only to define these exampleembodiments. Features or elements shown in various examples describedherein can be combined in ways other than shown in the examples, and anysuch combination is explicitly contemplated to be within the scope ofthe examples presented here. The following detailed description doesnot, therefore, limit the scope of what is claimed.

Regulating operation of the nervous system to characterize and improveorgan function includes in some examples introduction of a probe such asa needle, catheter, wire, or the like into the body to a specifiedanatomical location, and partially destroying or ablating nerves usingthe probe to destroy nerve tissue in the region near the probe. Byreducing nerve function in the selected location, an abnormallyfunctioning physiological process can often be regulated back into anormal range.

Unfortunately, it is typically very difficult to estimate the degree towhich nerve activity has been reduced, which makes it difficult toperform a procedure where it is desired to ablate some, but not all,nerves to bring the nervous system response back into a desired rangewithout destroying the nervous system response entirely.

One such example is renal nerve ablation to relieve hypertension.Various studies have confirmed that improper renal sympathetic nervefunction has been associated with hypertension, and that ablation of thenerve can improve renal function and reduce hypertension. In a typicalprocedure, a catheter is introduced into a hypertensive patient'sarterial vascular system and advanced into the renal artery. Renalnerves located in the arterial wall and in regions adjacent to theartery are ablated by destructive means such as radio frequency waves,ultrasound, laser or chemical agents to limit the renal sympatheticnerve activity, thereby reducing hypertension in the patient.

Unfortunately, renal nerve ablation procedures are often ineffective,such as due to either insufficiently ablating the nerve or destroyingmore nerve tissue than is desired. Clinicians often estimate based onprovided guideline estimates or past experience the degree to whichapplication of a particular ablative method will reduce nerve activity,and it can take a significant period of recovery time (3-12 months)before the effects of the ablation procedure are fully known.

Some attempt has been made to monitor nerve activity in such proceduresby inserting very small electrodes into or adjacent to the nerve body,which are then used to electrically monitor the nerve activity. Suchmicroneurography practices are not practical in the case of renalablation because the renal artery and nerves are located within theabdomen and cannot be readily accessed, making monitoring andcharacterization of nerve activity in a renal nerve ablation procedure achallenge.

Prior methods such as inserting electrodes into the arteries of apatient's heart and analyzing received electrical signals are notreadily adaptable to renal procedures, as arteries in the heart aregenerally large and more readily accommodate probes for performing suchmeasurements. Further, the cardiac electrical signals emitted from theheart are generally large and slow-moving relative to electrical signalsnear the renal arteries, which tend to be smaller in size and producesmaller signals that propagate more quickly through the nerves. As such,intravascular techniques used in heart measurements are readilyadaptable to similar renal processes.

Because nerve activity during organ procedures such as renal nerveablation cannot be readily measured, it is also difficult to ensure thatan ablation probe is located at the most appropriate sites along therenal artery, or to measure the efficiency of the nerve ablation processin a particular patient.

Some examples presented herein therefore provide an improved probe andmethod for characterizing nerve activity near an organ such as a kidney,including electrodes configured specifically to measure nerve activityin an environment different from the heart while permitting blood flowaround the probe. In a more detailed example, the probe includes a senseelectrode and a stimulation electrode that are expandable from a body ofthe probe, which can be introduced via a sheath. The sheath in a furtherembodiment comprises one or more electrodes, such as one or more senseelectrode reference or ground electrodes.

FIG. 1 illustrates an example of such a probe. Here, a probe assembly isshown generally at 100, including probe body 102, and first and secondhelical electrodes 104 and 106. Each of the helical electrodes isattached to the probe body at one end, shown here as an attachment point108, such as an epoxy bead or other suitable attachment mechanism. Theopposite end of each of the helical electrodes is constrained in theexample shown, such as by emerging through a hole in the probe as shownby helical electrode 106, and extends from the left end of the probeassembly to connect to electronic instrumentation to perform variousfunctions. The configuration of the helical electrode wires is such thatthe wires will expand about the axis of the probe body 102 when the wireof each helical electrode is forced toward the attachment points 108,causing the wire to form a circular shape having a diametersubstantially larger than the helical electrode wires in the collapsedposition, as shown at 100.

The probe assembly is shown again at 110, here with the helicalelectrode wires 104 and 106 forced toward the attachment points 108,causing the wire to expand away from the probe body 102. This helicalexpansion allows the helical electrodes to expand in an environment suchas an artery such as to contact the artery walls while allowing blood toflow around the probe body 102 and past the helical electrodes 104 and106.

Another example of a probe configured to characterize nerve activitynear an organ such as a kidney while permitting blood flow around theprobe is shown in FIG. 2. Here, a probe body is shown at 202, havingmesh electrodes 204 and 206 affixed thereto at attachment points 208.The mesh electrodes are substantially similar to the helical wireelectrodes of FIG. 1, except that several such electrodes are interwovento form a mesh that is closely wrapped around the probe body 202. Inthis example, each mesh electrode also has a sliding collar element 209located at the end of the mesh electrode opposite attachment point 208.

This sliding collar 209 when moved toward the attachment point 208causes the mesh to expand around the probe body 202, as shown generallyat 210. Here, the expanded mesh electrodes 204 and 206 are configured toprovide electrical contact, such as with an artery wall, in a diametersignificantly larger than the diameter of the probe body 202. Thisenables insertion of the probe body into an artery, and expansion of theelectrodes 204 and 206 to contact the artery walls, without blockingblood flow through the artery. Although the examples of FIGS. 1 and 2show two probe configurations that can achieve such functions, probeconfigurations other than those shown here may also be configured toachieve these or similar functions.

FIG. 3 illustrates one example of use of such a probe, in which a probe302 such as that shown in FIG. 1 or FIG. 2 is introduced into a bloodvessel, such as an artery 304, in a location near a body organ such askidney 306. The probe is introduced via a sheath in some examples, suchas where a sheath is advanced to the intended probe location in theartery, and then withdrawn sufficiently to expose the probe 302 to theartery 304. The probe 302 here comprises a stimulation electrode such aselectrodes 104 and 204 of FIGS. 1 and 2, and a sense electrode such aselectrodes 106 and 206 of the same Figures.

When deployed, the electrodes are expanded as shown at 308, such thatthey are near or touch the walls of the artery 304. The electrodes arethereby located nearer the nerve bundle 310 connecting the kidney to thecentral nervous system, as the nerve bundle tends to approximatelyfollow the artery leading to most body organs. As shown at 310, thenerve bundle tends to follow the artery more closely at the end of theartery closer to the kidney, while spreading somewhat as the arteryexpands away from the kidney. As a result, it is desired in someexamples that the probe is small enough to introduce relatively near thekidney or other organ, as nerve proximity to the artery is likely to behigher nearer the organ.

When in place, a practitioner can use instrumentation coupled to thesense electrode and stimulation electrode to stimulate the nerve, andmonitor for nerve response signals used to characterize the nervoussystem response to certain stimulus. In a further example, an ablationelement 308 is configured to ablate nerve tissue, such as by using radiofrequency, ultrasound, or other energy, such that the probe can activelystimulate the nerve and sense resulting neural signals in betweenapplications of energy via the ablation element 308, enabling moreaccurate control of the degree and effects of nerve ablation. In otherexamples, a probe 302 lacking an ablation element can be remove via thesheath, and an ablation probe inserted, with the ablation probe removedand the probe 302 reinserted to verify and characterize the effects ofthe ablation probe.

FIG. 4 shows an intraluminal microneurography probe and sheath assemblycoupled to associated instrumentation, consistent with an example. Here,a probe body 402 has an expandable sense electrode 404 and an expandablestimulation electrode 406, couple via wires to instrumentation. A sheath408 is used to introduce the probe into an artery or other biologicallumen or suitable location, and to carry instrumentation wires andmechanical connections used to manipulate the expandable electrodes. Theelectrodes are not shown here running through the sheath, but areinstead shown as schematic links between the electrodes and variousinstrumentation circuitry for clarity.

In this example, the expandable sense electrode 404 is coupled to asense circuit, such as a differential amplifier as shown at 410, withthe other input to the sense amplifier circuit coupled to a groundelectrode such as local ground electrode 412 coupled to the sheath 408.In another example, local ground electrode is located elsewhere, such ason the probe body 404. The expandable stimulation electrode 406 issimilarly coupled to a stimulation circuit 414 that is operable toprovide a stimulation voltage or current signal of a desired pulseshape, intensity, and duration to the expandable stimulation electrode406, with reference to body ground. Body ground is established in thisexample by a body ground electrode 416, which is here also shown ascoupled to the sheath 408, but which in other embodiments will takeother forms such as an electrode coupled to the body's skin. Here, thebody ground electrode 416 is further coupled to the local groundelectrode 412 by use of a low-pass filter, having a frequency responseor time constant selected such that the local ground electrode does notdrift significantly from the body ground level but retains the abilityto accurately detect and characterize local nerve impulses.

The electrodes in this example comprise electrical wires that aresignificantly smaller than are used in other applications such ascardiac probes, in part because the pulse duration in the nerve bundleleading to most body organs is typically much shorter than a cardiacmuscle excitation signal. In one embodiment, the sense electrode 404therefore comprises a wire or mesh of wires having a diameter of 8-10thousandths of an inch, while in other examples the wire diameter is5-10 thousandths, 5-15 thousandths, or any size under 15, 10, 8, or 5thousandths of an inch. The sense electrode is thereby configured toaccurately detect a typical nerve action potential of 2 millisecondstraveling at a meter per second without smearing or distorting themeasured pulse due to an overly large electrode.

The stimulation electrode in various examples comprises a wire or meshof wires having any of the above sizes, but in another example, it isdesired that the stimulation electrode 406 be substantially larger thanthe sense electrode 404 to avoid hyperpolarization of the nerve in theregion of the electrode during stimulation.

Wire size of electrodes such as the sense electrode 404 is selected infurther examples based on a typical nerve conduction velocity range of0.4-2 meters/second, with nerve impulses ranging from 1-3 milliseconds.Also, the sense electrode 404 and stimulation electrode 406 aredesirably placed a sufficient distance apart, such as 3 centimeters, toaccurately detect a typical nerve action potential of 2 millisecondswithout interference from the stimulation electrode.

Because the size of organ arteries such as the renal artery aretypically in the range of 5 millimeters in diameter, it is desired tohave a probe body that is a fraction of this size, such as having adiameter of 2.5 mm, 2 mm, 1 mm, or similar. This enables introduction ofthe probe without interfering with blood flow through the artery, suchthat the expandable electrodes can still expand to the artery wallswithout further significantly impeding blood flow.

An intraluminal microneurographic probe such as those shown in FIGS. 1-4can therefore be introduced into an artery via a sheath, and used tomonitor nerve activity during normal operation of an organ. This enablescharacterization of nerve activity in the organ, such as to diagnose ortreat a variety of conditions. In one such example, a probe is used forcharacterization of overactive nerves reaching the kidney in patientssuffering from hypertension, and to monitor ablation of the nerves to apoint where nerve activity is in the desired range as measured using theprobe. In other examples, the probe may be used while other actions areperformed, such as to monitor nerve activity to a patient's prostatewhile surgery or other methods remove material to treat prostate canceror enlarged prostate problems. Because it is desirable that significantnerve connection to the prostate be preserved during such procedures, aprobe such as those presented here can be used to minimize the chancesof nerve damage that may affect normal function of the prostate.

A probe such as those shown here can also be used to diagnose variousorgan dysfunctions, such as where an organ overreacts to nerve impulsesor overstimulates the nerve in response to organ activity. The probe ishere described in some examples as an intraluminal probe, meaning theprobe may be introduced into various lumina or pathways in the body,such as arteries, veins, the gastrointestinal tract, pathways ofbronchii in the lungs, pathways of the genitourinary tract, and othersuch pathways. The probe is neurographic in the sense that it enablescharacterization, such as measurement, recording, and visualization ofneurologic activity in the vicinity of the probe. Because the autonomicnervous system regulates a wide variety of functions within the body,including circulation, digestion, metabolism, respiration, reproduction,etc. by a network of parasympathetic and sympathetic nerves thattypically accompany the blood vessels supplying blood to the organs theyregulate, an intraluminal neurographic probe such as those describedhere can be used to measure or characterize the regulation of many ofthese functions by introducing the probe into the blood vessels near theorgan of interest.

Although the example of FIG. 3 illustrates ablation of nerves near thekidney to regulate kidney function in treating hypertension, nervesregulating liver function accompany the hepatic artery and the portalvein, nerves regulating the stomach accompany the gastroduodenalarteries, nerves from the superior mesenteric plexus accompany thesuperior mesenteric artery and branch to the pancreas, small intestineand large intestine, and nerves of the inferior mesenteric plexusaccompany the inferior mesenteric artery and branch to the largeintestine, colon and rectum. These examples illustrate other organs thatcan be characterized and regulated using probes and techniques such asthose described herein.

In treating kidney function, it is significant that renal sympatheticnerves have been identified as a major contributor to the complexpathophysiology of hypertension. Patients with hypertension generallyhave increased sympathetic drive to the kidneys, as evidenced byelevated rates of the renal norepinephrine “spillover.” It is thereforebelieved that ablating renal sympathetic nerve function with sufficientenergy will cause a reduction in both systolic and diastolic bloodpressure, relieving hypertension in the patient.

Studies have shown that most nerves surrounding the renal arteries arewithin two millimeters of the renal artery, with nerves clustered moreclosely around the artery near the kidney, making measurement andtreatment of the nerves from the renal artery practical. But, ascomplete destruction or ablation of the nerves is likely not desirable,monitoring nerve activity during or between nerve ablations, such as viathe probes described herein, is an important tool in characterizing andregulating the degree to which nerve activity has been reduced. Beforeintroduction of probes such as those described here, clinicians wereunable to readily determine extent of renal sympathetic nervemodification during a procedure in a clinically relevant timeframe, andcould not measure durability of nerve damage during follow-up periodafter denervation. Now, with probes such as those described hereinavailable, a clinician can take such measurements, and can to assesshealth of renal sympathetic nerves pre-procedurally to select or screenpatients for denervation.

In operation, a clinician can measure nerve activity such as renalsympathetic nerve activity (RSNA) by emitting an electrical pulsethrough stimulation electrodes in the probe, and recording propagationalong renal sympathetic nerve fibers using the sense electrode orelectrodes on the probe. The clinician can then compare RSNA pre- andpost-denervation to determine the degree of nerve ablation incurred,thereby more accurately achieving the desired degree of nerve ablationduring treatment of the patient. More specifically, a clinician canapply an electrical stimulus to a site in the proximal renal artery, andthen monitor or record the nerve activity between the stimulus site andthe kidney, thereby measuring the resultant downstream action potentialin the nerve. Nerve ablation is then performed, and the stimulus andmeasurement of the nerve is repeated to verify a reduced or eliminatedevoked potential detected in the nerve as a result of stimulation viathe probe's electrodes.

The probe system described in the examples here can therefore providereal-time feedback on functionality of renal sympathetic nerves,providing integrated evaluation of all nerve fibers surrounding a renalartery, at the artery proximal, distal, and renal branch locations. Theprobe is easily deployed via catheter-based delivery, and can be used asa standalone product or integrated with an ablation element. The probesystem's low hardware and software costs and easy learning curve forclinical users make the probe system well-adapted for widespreadadoption for treatment of nerve conditions such as those describedherein.

A variety of experiments have been conducted to verify operation ofprobes such as those described herein, including using an isolatedcanine/porcine kidney and the associated vasculature to conduct certaintests. In one such test, probes such as those of FIGS. 1-4 were used toverify renal nerve health by measuring spontaneous renal sympatheticnerve activity (RSNA) using intraluminal microneurography, demonstratingthat such probes cause effective stimulation and recording of RSNA. Inthe tests, stimulus-elicited response established a baseline recordingof RSNA, and the circumferential section of renal nerve fibers weredamaged using a scalpel. Remeasuring the stimulus-elicited response andcomparing the response to the established baseline recording of RSNAconfirmed that spontaneous sympathetic renal nerve activity had beenreduced.

FIG. 5 shows spontaneous nerve activity, measured from the wall of therenal artery of an explanted kidney. Here, the measurements are takenusing needles placed in the wall of the renal artery, using relativelyinvasive microneurography techniques.

FIG. 6 shows spontaneous nerve activity in the wall of the renal arteryof an explanted kidney, using an intraluminal microneurography probe.Here, the peak signal levels are somewhat reduced relative to the methodof FIG. 5, but accurate detection, measurement, and recording ofspontaneous RSNA signals is shown to be achieved.

In FIG. 7, a stimulus signal (top) and the resulting measured RSNAaction potential are shown. Here, the renal nerve RSNA action potentialis measured using needles in the artery wall, using a stimulus time ofapproximately 1.3 milliseconds, configured to avoid overlapping thestimulus and response signals based on the expected conduction velocityand the selected stimulus and sense electrode spacing.

Subsequent testing on live animals also proved successful, with a seriesof experiments conducted in a live rat model to confirm detection ofrenal sympathetic nerve activity (RSNA) in a living animal withcompeting signals from cardiac electrical activity and respiratorymovement. Excellent results were achieve using probes havingconfigurations such as those described herein, based on an experimentalprocedure in which an evoked RSNA baseline was determined in the intactrenal artery, and RSNA was measured as the renal artery was transected.

Destruction of the renal sympathetic nerves, and the resulting effectson RSNA signals measured as a result of an applied stimulus signal, areshown in FIG. 8. Here, ten sets of data are overlaid to generate a graphrepresentative of typical levels and distribution of RSNA response to astimulus signal as varying degrees of arterial transection. At 802, theevoked RSNA baseline measurements taken prior to cutting across theartery are taken as a reference. At 804, the artery is 50% transected,resulting in significant reduction in observed RSNA response, and at806, the artery is 100% transected, and little to no RSNA response isobserved. In this example, transection of the renal arteries was used todestroy renal neural pathways because rat renal arteries are too smallfor effective radio frequency ablation.

FIG. 9 is a flowchart illustrating a method of using an intraluminalmicroneurography probe to treat a medical condition, consistent with anexample. As shown generally at 900, a method of treating a medicalcondition involves using probe to excite and measure nerve activity nearan organ, and selectively ablating nerve tissue near the probe until thedesired nerve activity in response to the excitation is observed.

A sheath carrying the probe into the artery is inserted at 902, and isadvanced to a location in the artery near a body organ that is thesubject of the medical condition and treatment, such as treating akidney's neural sympathetic response to treat hypertension. The sheathis withdrawn slightly at 904, exposing at least part of the probeincluding an expandable sense electrode and an expandable stimulationelectrode to the artery. At 906, the expandable stimulation and senseelectrodes are expanded, such that the electrodes contact the arterialwall while permitting blood flow around the probe and the electrodes. Atthis point, the probe is properly deployed and ready to performmeasurement.

The expandable stimulation electrode is excited at 908, inducing anelectrical signal into the nerves adjacent to the arterial wall. Thenerves propagate the signal from the stimulation electrode, which can beobserved at 910 as sympathetic nerve activity as a result of excitingthe stimulation electrode. The observed sympathetic nerve activity canthen be measured, characterized, stored, viewed, etc., to determinewhether the sympathetic nerve activity exceeds a desired level at 912.If a desired level of sympathetic nerve activity is exceeded, nervesproximate the probe are ablated at 914, such as using an ablationelement comprising a part of the probe located between the senseelectrode and the stimulation electrode. Steps 908-912 are thenrepeated, until the sympathetic nerve activity is determined not toexceed the desired level at 912. At that point, the measurement andnerve ablation is complete, and the probe and sheath can be withdrawn at916.

Although the examples presented here primarily illustrate measurement ofsympathetic nerve activity using the probe systems described, probesystem such as those illustrated here can also be used to monitor organactivity, pain, or other nervous system indicia. For example, pain canbe monitored during surgery in some applications, or nerve activity canbe measured while externally stimulating an organ.

Although specific embodiments have been illustrated and describedherein, any arrangement that achieve the same purpose, structure, orfunction may be substituted for the specific embodiments shown. Thisapplication is intended to cover any adaptations or variations of theexample embodiments of the invention described herein. These and otherembodiments are within the scope of the following claims and theirequivalents.

1. An intraluminal microneurography probe, comprising: a probe body thatis substantially cylindrical and having a diameter and a length that isperpendicular to the diameter, the probe configured to be introducedinto an artery near an organ of a body without preventing the flow ofblood through the artery; an expandable sense electrode, fixed to theprobe body at one end of the sense electrode and movable relative to theprobe body at a second end of the sense electrode such that movement ofthe movable end toward the fixed end causes the sense electrode toexpand from the probe body toward a wall of the artery; an expandablestimulation electrode, fixed to the probe body at one end of thestimulation electrode and movable relative to the probe body at a secondend of the stimulation electrode such that movement of the movable endtoward the fixed end causes the sense electrode to expand from the probebody toward a wall of the artery; a ground electrode configured tocouple to the body; a plurality of electrical connections operable toelectrically couple at least the expandable sense electrode, expandablestimulation electrode, and ground electrode to electrical circuitry. 2.The intraluminal microneurography probe of claim 1, wherein the senseelectrode wire is equal to or smaller than 10 thousandths of an inch ina direction of nerve propagation.
 3. The intraluminal microneurographyprobe of claim 1, wherein at least one of the expandable sense electrodeand the expandable stimulation electrode comprises an expandable mesh.4. The intraluminal microneurography probe of claim 1, wherein at leastone of the expandable sense electrode and the expandable stimulationelectrode comprises an expandable wire helix.
 5. The intraluminalmicroneurography probe of claim 1, wherein the diameter of the probebody is 2 mm or less.
 6. The intraluminal microneurography probe ofclaim 1, wherein the expandable sense electrode and the expandablestimulation electrode have fixed points on the probe body that arebetween two and four centimeters apart along the length of the probebody.
 7. The intraluminal microneurography probe of claim 1, wherein theground electrode is configured on or near the probe body.
 8. Theintraluminal microneurography probe of claim 1, further comprising asecond ground electrode such that separate sense ground and stimulationground electrodes are provided.
 9. The intraluminal microneurographyprobe of claim 1, wherein the separate sense ground and stimulationground electrodes are coupled to one another via a low-pass filter. 10.The intraluminal microneurography probe of claim 1, further comprising asheath assembly operable to guide the probe into position within theartery.
 11. The intraluminal microneurography probe of claim 10, whereinthe ground electrode is coupled to the sheath.
 12. The intraluminalmicroneurography probe of claim 11, further comprising a second groundelectrode couplable to the body such that separate sense ground andstimulation ground electrodes are provided
 13. The intraluminalmicroneurography probe of claim 11, wherein the ground electrode coupledto the sheath and the second ground electrode couplable to the body arecoupled to one another via a low-pass filter.
 14. The intraluminalmicroneurography probe of claim 1, further comprising a neural ablationelement attached to the probe body.
 15. The intraluminalmicroneurography probe of claim 14, wherein the neural ablation elementis attached to the probe body at a location between the expandable senseelectrode and the expandable stimulation electrode.
 16. A method ofcharacterizing nerve activity associated with a body organ, comprising:introduction of a probe into artery to a location proximate to the bodyorgan; expansion of an expandable sense electrode and an expandablestimulation electrode comprising a part of the probe to contact theartery wall while permitting blood flow around the expanded sense andstimulation electrodes; excitation of the stimulation electrode using anelectricity source coupled to the stimulation electrode; and measurementof sympathetic nerve activity as a result of exciting the stimulationelectrode using the expanded sense electrode.
 17. The method ofcharacterizing nerve activity associated with a body organ of claim 16,further comprising ablation of nerves in the vicinity of the locationproximate to the body organ.
 18. The method of characterizing nerveactivity associated with a body organ of claim 17, where ablation isperformed via an ablation element comprising a part of the probe. 19.The method of characterizing nerve activity associated with a body organof claim 17, further comprising re-excitation of the stimulationelectrode using an electricity source coupled to the stimulationelectrode, and re-measurement of sympathetic nerve activity as a resultof exciting the stimulation electrode using the expanded sense electrodeto confirm the effects of the ablation
 20. The method of characterizingnerve activity associated with a body organ of claim 16, whereinintroduction of the probe into the artery comprises introducing theprobe into the artery via a sheath.